The invention relates to a method for operating a fuel supply system and especially a fuel supply system of an internal combustion engine of a motor vehicle wherein the fuel is pumped into an accumulator with the aid of a pump and wherein the fuel pressure is adjusted to at least a first pressure P1 or a second pressure P2.
German patent publication 198 18 421 discloses a fuel supply system having two fuel pumps connected in series and fuel valves injecting directly into the combustion chamber. A pressure control valve and a valve device are provided in a fuel supply line. The pressure control valve and the valve device are hydraulically connected to operate one behind the other. A second pressure control valve is provided in a further fuel line. The pressure, which is controlled by the second control valve, is significantly higher than the pressure held by the first pressure control valve. -he first pressure control valve controls the pressure on its input end, for example, to 3 bar. The second control valve is, for example, adjusted to a pressure of 9 bar. The valve device has a first switching position and a second switching position. In the first switching position, fuel can flow through the fuel line via the pressure control valve. The fuel line is cut off when the valve device is in its second switching position.
The valve device is in its first switching position in the normal operating state of the engine, that is, after conclusion of the starting operation of the engine and when the fuel temperature is not too high. The fuel pressure in the fuel connection is determined by the first pressure control valve when the valve device is in its first switching position. The first pressure control valve ensures that, in the normal operating state, the fuel pressure is held to be correspondingly substantially constant at a normal value, for example, 3 bar.
During the starting operation (that is, at an increased fuel temperature), the valve device is in the second switching position wherein the fuel path for the fuel through the fuel line is closed. When the fuel line is closed, the second pressure control valve determines the magnitude of the fuel pressure in the fuel connection.
It is an object of the invention to provide a reliable diagnostic method for a fuel supply system such as for an internal combustion engine of a motor vehicle.
The method of the invention is for operating a fuel supply system including a fuel supply system of an internal combustion engine for a motor vehicle. The method includes the steps of: pumping fuel with a pump into an accumulator wherein the fuel is under pressure; adjusting the fuel pressure to at least a first pressure (P1) and detecting a first pressure signal (PS1); adjusting the fuel pressure to at least a second pressure (P2) and detecting a second pressure signal (PS2); forming a pressure difference (xcex94P) from the first and second pressure signals (PS1, PS2); and, recognizing and storing a fault in the fuel supply system when the pressure difference (xcex94P) deviates from an expected pressure difference (xcex94P_E) by more then a threshold value (S).
An especially significant advantage of the invention is that a precise diagnosis of the fuel supply system is achieved without additional components.
A further advantage is that the diagnosis is possible with the aid of a fuel pressure sensor mounted in a high pressure region.